1. Field of the Invention
The present invention relates to an optical system, and is suitable, for example, for a projection optical system configured project image information onto a predetermined surface for a liquid crystal projector or an image pickup optical system of a camera.
2. Description of the Related Art
An optical system for a liquid crystal projector is demanded to be a high angle-of-view projection optical system configured to project a high definition image on a large screen with a small distance. An optical system for an image pickup apparatus, such as a camera, is demanded to be an image pickup optical system having a long back focal length, a high image quality, and a high angle of view configured to shoot a wide subject range. In order to obtain a high definition projected image and a high quality captured image, a color shift (or chromatic aberration) mitigation among a variety of aberrations of an optical system is important. In general, using a lens made of anomalous dispersion glass is effective to correct the chromatic aberration while maintaining a size of the entire optical system.
On the other hand, for the optical system having a wide angle of view, it is effective to configure the entire lens system to be a retrofocus type in which a lens unit of a negative power is located on the enlargement conjugate side (the object side). U.S. Patent Publication Application No. 2002/0005994 proposes a retrofocus type optical system configured to correct a chromatic aberration using a lens made of anomalous dispersion glass. However, simply using a lens made of an optical material of the anomalous dispersion for the optical path has a difficultly in obtaining a good performance over a screen while well correcting the chromatic aberration.